CHARACTERIZATION OF HUMAN-B CREATINE-KINASE GENE-REGULATION IN THE HEART IN-VITRO AND IN-VIVO

During cardiogenesis, genes indicative of the adult phenotype are tran scriptionally activated while genes characteristic of the embryonic ph enotype are down-regulated. The regulation of embryonic genes such as the brain isoform of creatine kinase (BCK) during cardiac development has not been characterized. Accordingly, the transcriptional regulatio n of BCK in the developing heart was determined. In vitro and in vivo promoter analyses of the human BCK gene identified an element between +25 and +57 that functioned as an enhancer. Electromobility shift assa ys using adult and neonatal nuclear extracts identified a specific com plex binding this element, the abundance of which correlated with the developmental level of endogenous cardiac BCK expression. Mutations at +47 and +53 led to a loss of activity in transfected cells and obviat ed binding in electromobility shift assays. These data show that a nuc lear factor in cardiocytes interacts with an enhancer element (+25 and +57), via nucleotides +47 and +53, to drive BCK expression in the hea rt and suggest that developmental BCK expression is via abundance of t his factor. The nuclear factor has not been identified but as describe d previously binding sites are not present in the enhancer, it is eith er a known factor interacting with a new recognition site or a new fac tor.